JVM and OOPS Introduction

static Keyword :◦ The static keyword is used in java mainly for memory

management.

Types Of Static Members :◦ Java supporting four types of static members

1. static variables2. static blocks3. static methods4. main method

Non-static Members :◦ Class level members which don’t have static keyword in their creation statement are called non-static members.

Types Of Non-static Members :◦ Java supporting four types of non-static members

1. Non-static variables2. Non-static blocks3. Non-static methods4. Constructors

Package:◦ It is a Java folder used to group related classes , interfaces

and enums.

Class :◦ Class is a collection of data members and member functions

Interface :◦ Interface is a fully unimplemented class , it is used for

defining set of object operations.

Abstract Class :◦ A class that is declared with abstract keyword, is known as

abstract class in java

DataType :◦ Data type gives information about size of the memory

location and range of data that can be stored inside that location .

1. Primitive types2. Referenced types

Primitive Types: ◦ Primitive Data types is used to store single value at a time.

Size and Default value of Primitive type:

Data Type Name Size [ byte( s ) ] Default Value

byte 1 0

short 2 0

int 4 0

long 8 0

float 4 0.0

double 8 0.0

char 2 ‘\u0000'

boolean 1 false

Types of Loop :◦Java has very flexible three looping mechanisms.

1. while loop2. do…while3. for loop

 Enhanced for Loop :  Syntax :

for (data_type variable: array_name){ --------- --------- }

Switch-case:◦ A switch statement allows you to test the value of an

expression and, depending on that value, to jump directly to some location within the switch statement.

Syntax: switch (expression) { case value1: //statement s break; ------------------------ case value n: //statements default: //default statement sequence }

Using String in Switch-case:◦ In Java SE 7 and later, you can use a String object in

the switch statement's expression. 

 Use of instanceof keyword:◦ The instanceof operator allows you to determine the type of

an object. Example:- if(employee instanceof Person){ --------------------- --------------------- }

Class:oA class can be defined as a template/blue print that describes

the behaviours/states that object of its type support. Syntax to declare a class: class <class_name>{       data member;       method;   } Object:

◦ object is the physical reality of a class. Object’s characteristics : 1.State 2.Behaviour 3.Identity

Relationship with Objects:◦ Java supports three types of relationship:

1.IS-A.(Inheritance) 2.HAS-A.(Composition) 3.USES-A.(Aggregation)

OOPs Features:◦ We have mainly four OOPs Features:

1.Encapsulation 2. Inheritance 3. Abstraction

4. Polymorphism

Encapsulation:◦ The process of creating a class by Hiding internal data from

the outside.

Inheritance:◦ The process of creating a class to reuse exited class member

using our class name or objects is called inheritance.

Abstraction :◦ The process of defining a class by providing necessary

details to class objects operation by hiding or removing its implementation details called abstraction.

Polymorphism:◦ The process of defining a class by with multiple methods

with same name but different implementation is called polymorphism.

Types of Polymorphism: 1. Compile-time polymorphism.

2. Run-time polymorphism.

Behaviors of Polymorphism: ◦ we can developed polymorphism by using

1. Method Overloading. 2. Method Overriding

Return Type Declaration:◦ Use the return statement to return the value.◦ Declare a method's return type in its method declaration. ◦ Declare Within the body of the method.

Types Of Constructor:◦ Default constructor (no-argument constructor):

A constructor that have no parameters Ex-

◦ Parameterized constructor: A constructor that have parameters 

Constructor Overloading:◦ A class can have any number of constructors that differ in

parameter lists. Constructor Chaining:

◦ Calling one constructor from other.

this Keyword:◦ this is a reference variable that refers to the current object.

super Keyword :◦ super is a reference variable that is used to refer immediate

parent class object.

Array:◦ Array is a collection of similar type of elements that have

continuous memory location. Array Declaration:

◦ 1 Dimensional Declaration- Ex-int[] x;

◦ 2 Dimensional Declaration- Ex-int[][] x;

Array Initialization :◦ Syntax- Datatype arrayName = new datatype[size];

Array Assignment :◦ Syntax- DataType[] arrayRefVar = {value0, value1, ..., value

k}; Anonymous Array:

◦ Array without any name.◦ Syntax- new datatype[]{10,20,30};